D3D: Reset current descriptor tables when changing root sig.
D3D: Reset current descriptor tables when changing root sig.

If we switch from a root signature with samplers/textures to one without
and then back, the descriptor tables associated with them are unbound on
the command list, but we don't reflect that in our tracking of the
current descriptor table.

Change-Id: Ibd3891152f1beab10c20caa1f2aaec0cd59e519e
Bug: skia:9935
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317656
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Auto-Submit: Jim Van Verth <509afb0bfbb23ecaaf1fb3323209f531b45e75a6@google.com>

aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia